Laser cathode-ray tube

ABSTRACT

A laser cathode-ray tube having an electron beam source, a means for its control, and a laser target containing a supporting substrate, a cavity resonator formed by two mirrors and multilayer semiconductor structure having active and passive strained layers, whose difference in lattice parameters in a free state is up to 10% or more and which have coherent boundaries between each other in the structure.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to Applicant's Russian application SerialNo. 92014713/21, filed Dec. 28, 1992 and International applicationSerial No. PCT/RU/00318, filed Dec. 27, 1993 on which Applicants claimforeign priority under 35 U.S.C.§§119 and 365.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to Applicant's Russian application SerialNo. 92014713/21, filed Dec. 28, 1992 and International applicationSerial No. PCT/RU/00318, filed Dec. 27, 1993 on which Applicants claimforeign priority under 35 U.S.C.§§119 and 365.

FIELD OF THE INVENTION

The invention belongs to the field of quantum electronics and electronicengineering and may be used in devices where a scanning light beam isused, more particularly in television projector systems.

BACKGROUND OF THE INVENTION

A prior art laser cathode-ray tube being in fact a scanningsemiconductor laser with longitudinal pumping by an electron beamcomprises a source of an electron beam and a means for its control, andalso a laser target which is a semiconductor member with mirrorcoverings, which forms an optical resonator. The laser target is gluedto a heat removing substrate which is transparent to a generated laserbeam (A.S.Nasibov. "Laser cathode-ray tube--new device of the quantumelectronics".--Bulletin of the Academy of Sciences of the USSR, No.9,pp.48-56). The electron beam penetrates through one of mirrors intosemiconductor member, excites some region of this member wherein itcauses nonequilibrium current carriers--electron-hole pairs, whichrecombine with emitting light. The optical gain aroused in this excitedregion and optical resonator generates the laser beam. The laser beam isgenerated from a spot on the laser target where the focused electronbeam to be located. The laser beam scanning and modulation of itsintensity are made by scanning of the electron beam and changing itscurrent.

The main disadvantage of this device is that high efficiency and longlifespan of the laser target can only be achieved simultaneously only atcryogenic temperature. The reason is due the to level of excitation ofsemiconductor member with electron beam pumping is very non-uniform overthe volume of the member. Thus, if a semiconductor member is used whichhas a thickness of more than the average depth of the electron beamexcitation of the target, there are parts of the member which arelittle-excited or not excited at all. These parts, however, absorb lightemanating from the high-excited parts. This is especially true when themember is at temperatures higher than cryogenic temperatures. Thisdecreases laser efficiency and the lifespan of the member. If a thinnersemiconductor member is used the laser efficiency may be high enough andin some cases electrons can to penetrate through the member and partlytransparent mirror covering into glue layer and destroy it, making thelifespan small.

Another kind of prior art laser cathode-ray tube has a laser target madeof a semiconductor with a two-layer structure (A. A. Matyash et al,"Semiconductor laser with longitudinal electron pumping", USSR PatentNo.1034569, issued Nov. 2, 1981 and described in a paper by V. N. Katsapet al., "Heterostructures CdS_(x) Se_(l-x) /CdS in Lasers withLongitudinal Pumping by Electron Beam", Sov. J. of Quantum Electronics,1997, Vol.14, pp.1994-1997). The layer of CdS_(x) Se_(l-x) with narrowerbandgap is pumped by an electron beam and its thickness is approximatelyequal to the typical depth of penetration of an electron beam into alaser target. The wider bandgap layer of CdS has thickness several timeslarger and performs two functions: on one hand, it separates partlytransparent mirror covering and glue layer from the zone of electronbeam pumping, and therefore increases the lifespan of laser target, onthe other hand, this layer having wider bandgap does not absorbgenerated emission and allows, therefore, an increase in the operatingtemperature of the laser target. The problem is that it is verydifficult to make this device with an adequate efficiency becausecenters of non-emitting recombination are formed near the interfaceboundary (heteroboundary) between two relatively thick semiconductorlayers made of II-VI compounds and laser efficiency is rather low (3% at300 K.).

The nearest prior art to the present invention is a laser cathode-raytube consisting of a source for an electron beam, a means forcontrolling the beam, and a laser target which includes two mirrorsforming optical resonator, a semiconductor medium located between themirrors, and a substrate for optical resonator (E. I. Gordon et al, U.S.Pat. No.4,539,687 of Sep. 3, 1985, Int.Cl. HOIS 3/19). The semiconductormedium is comprised of a three-layer heterostructure of lattice-matchedIII-V compounds. Heterostructure is defined to mean a structure withatomic bonds between its layers which are made of different crystallinematerials. Lattice matching means that the crystal structures of thesecompounds are identical in that their crystal lattice parameters differnot more than about 0.1%. This is an important condition of growing aheterostructure with a low number of structure defects, because such astructure can be used for achieving high laser efficiency at roomtemperature.

The disadvantage of the Gordon device is that the lattice-matchingrequirement severely restricts the choice of semiconductor compoundswhich can be used for defectless or low defect heterostructure laserswhich are to be stimulated with longitudinal pumping by the electronbeam. Additionally, such lasers can only be constructed for use ininfrared spectral region because they are based on semiconductorcompounds, such as GaAs and AlAs, which have lattice periods that differby less than 0.1%. However, even in the case of GaAlAs-laser, itsefficiency is still not high enough (see E. I. Gordon et al).

SUMMARY OF THE INVENTION

It is an object of the present invention to construct a laser targetthat would achieve high efficiency of lasing with a long lifespan inlaser cathode-ray tube using a broad class of semiconductor compounds.

Another object of the invention is to increase of the efficiency of thelaser cathode-ray tube which emits light in visible and near ultravioletregions of spectrum with the laser target operating at the roomtemperature.

These and other objects are accomplished in a laser cathoderay tubecomprising a source of an electron beam, a means of its controlling thebeam, and a laser target, which consists of two mirrors forming ancavity resonator, a semiconductor structure placed between the mirrors,and a supporting substrate for the resonator. According to theinvention, the semiconductor structure comprises elastic strainedelements which crystal parameters in a free state differ by up to 10% ormore but their proportions are adapted so that these elements havecoherent boundaries in the structure.

More specifically, in order to achieve acceptable laser parameters atroom temperature the present invention uses a semiconductor perfectstructure having active and passive elements with different bandgaps. Amain idea of the invention is that this perfect structure is not made ofsemiconductor crystalline materials having an identical structure andpractically identical (matched) parameters of crystal lattice (a groupof such materials being very small) but is made of materials selectedfrom a group consisting of crystalline compounds which crystal latticeparameters differ by up to 10% or more, and structure elements made ofthese materials are small enough to make a perfect structure. A perfectstructure means an absence of any structural defects at or nearboundaries between the structure elements. This occurs if the crystallattice periods of two adjacent elements are equal to each other alongtheir interface. In other words, the structure's elements have coherentboundaries. These elements are also strained in the structure because oftheir materials have essentially different crystal lattice periods whenthey are in a free state.

In order to simplify the design and the manner of manufacturing, thestructure is made planar with mirrors that are coated on the oppositesides of the semiconductor structure, so a perpendicular to thesemiconductor structure is the longitudinal axis of the resonator, andthe strained elements are formed as strained layers orientedperpendicular to the axis of the resonator. The thicknesses of thelayers depend on the degree of the lattice mis-matching which occurs inthese layers in a free unstrained state. The less is this mismatching,the more can be the thickness of these layers. Each occurrence ofmis-matching places a limit on the thickness of each layer and an excessof thickness will result in the appearance of structural defects, suchas a mis-matching dislocation at the boundaries of these layers, and theboundary become incoherent (J. W. Matthews and A. E. Blackeslee. J.Crystal Growth. 1974, Vol.27, p.118). The appearance of the mis-matchingdislocation decreases elastic strainings in the structure layers. Theseelastic strainings increase with increasing of the thicknesses ofadjacent structure layers up to the thickness limit. It important tonote that if the boundaries between the layers are incoherent, thelasing threshold of the laser target increases and the efficiency oflasing decreases. This results in decreasing of the power and thebrightness of the laser cathode-ray tube.

In the laser targets made of semiconductor compounds which crystallattice parameters differ by more than 10%, it is more preferable toinclude at least one layer with the thickness of a monolayer.

One of the important differences of the present laser target from theinjection semiconductor lasers, wherein strained layer heterostructuresare used, is that all of the dimensions of the present semiconductorstructure are larger. This is especially true regarding structurethickness. The main reason is that the excited region of the lasertarget is determined by the penetration depth of the electron beam whichcan exceed 10 μm in high-power projector cathode-ray tubes. In theexcited region of injection lasers is determined by the free path lengthof nonequilibrium carries which is less the 1 μm. Therefore, all mainelements of the laser target have sizes from 0.5 to 10 μm or moreperpendicular the structure layers. On the other hand, the majority ofknown semiconductor materials used in laser targets, especially thosewhich emit light in the visible or ultraviolet regions of the lightspectrum have difference of the lattice parameters of several percents.In the case of this large mis-matching, the thickness limit is less than10 nm. In order to make a perfect semiconductor structure of thesematerials, it should consist of several dozens, or even hundreds ofstrained layers which thicknesses are less than the thickness limit. Inthis case, in order to simplify the design of the laser target and thetechnology of its manufacturing, it is worthwhile to use a plurality ofalternating strained layers of two or more compounds, these layershaving constant thicknesses, and forming a one-dimensional superlattice.(This means that a crystal lattice having basic crystal periods hasadditional periodic alternation of atoms along one of directions. Ofcourse, this additional periodic alternation results in small variationof basic crystal period along this direction.) In most cases it isenough that only directly excited region is made like one-dimensionsuperlattice, but for increasing lifespan of laser target it ispreferable to do whole semiconductor structure and also one of themirrors in this way. Note also that a one-dimensional superlattice oftwo or more crystal compounds possesses new properties which candecrease the lasing threshold and increase the efficiency of lasercathode-ray tube as a whole.

In order to get emission in the region from near infrared to nearultraviolet spectral region, it is worthwhile that elements ofsemiconductor structure are made of at least two compounds selected fromgroup consisting of II-VI and III-V compounds, and their solidsolutions. These compounds should have energy gaps differing from eachother by at least 7 mev. Because the laser targets work mainly attemperatures higher than 80 K. (approximately 7 mev in energy), themanufacturing of laser targets from heterostructure with a difference ofenergy gaps of its elements less than 7 mev, will not result inimproving of lasing characteristics in comparison to the ones of lasertargets with uniform active semiconductor medium, but will result onlyin complicating of the manufacturing process.

One-dimensional varizone superlattice is the simplest to manufacture,and it is preferable to making semiconductor structure of crystalcompounds having small mis-matching of the crystal lattice. In thiscase, the additional periodic alternation of atoms of the superlatticeoccur gradually along one of the directions. It results in anappropriate gradual change of bandgap. This change can be achieved bymeans of either change of chemical composition of the solid solutionwhich is used or by changing the density and the type of doping. Anexample of a varizone superlattice may be a structure having alternativelayers of two binary compounds which have boundaries between each other,which are not sharp, but smooth. Growing of such structures is simpleenough and has the advantage of producing a laser target with a varizonesuperlattice is that is inexpensive to manufacture with inexpensive andmore productive growing equipment.

More complicated in manufacturing but the most effective in decreasingof lasing threshold and increasing of efficiency of the laser target isa laser target which has the following design: each second layer of amultilayered semiconductor structure has a constant thickness and ismade of a semiconductor of the same composition, and the first and allsubsequent intermediate layers have different thicknesses and are madeof solid solution of semiconductor binary compounds of one type, havingenergy bandgap wider than every second layer, and the composition ischanged in correspondence with the thickness of the layer by the valuenecessary for establishing crystal lattice period common for all layersalong these layers.

The main point of this invention is that it is necessary to use in thelaser generation as much as possible energy of nonequilibrium carriersof the slightly excited regions of semiconductor structure, the presenceof which is the consequence of nonuniformity of excitation of lasertarget in the laser cathode-ray tube. Therefore, it is preferable thatthe sum of thicknesses of two neighbor active and passive layers of thesemiconductor structure be changed along the longitudinal axis of theoptical cavity inversely proportionally to the part of energy ofelectron beam absorbed by these two layers. In this case it isworthwhile to achieve the period of crystal lattice along the layerscommon for all layers, which provides a perfect semiconductor structurewith high efficiency. Such semiconductor structures are made of layersof constant composition of a first binary compound and layers withvariable composition which are made of solid solution of the firstbinary compound and a second binary compound with the molar content ofthe second binary compound in the solid solution in each layer withvariable composition varying depending on the thickness of the layeraccording to the following equation:

    x=C·{ 1+D·(1+h.sub.1 /h.sub.2).sup.0.5 !-1}(1)

where x is the molar content of the second compound in the solidsolution, h₁ is the constant thickness of the layers of the firstcompound, h₂ is the variable thickness of the solid solution, and C andD are the positive numbers that depend on the choice of the first andsecond compounds and the crystal lattice period of the structure withstrained layers along the layers.

In all cases it is worthwhile to choose the proportions of thesemiconductor structure and the energy of the electron beam beingmutually adapted so that the part of the electron beam energy, absorbedin the structure, is not less than 50%. In the case of a planarsemiconductor structure, this condition corresponds to a choice of thestructure thickness being more than about 0.2 electron straightened pathlength in the semiconductor structure R_(o). This value is usually usedfor characterization of electron dispersion process in different media.(Each electron penetrating into a solid state medium collides withmedium atoms, giving up a part of its energy to these atoms, beforemoving along a broken curve up to a full stop. The total length of thisbroken curve is R_(o).) It should be noted that specific excitationdepth of the medium is usually 4 to 5 times less than R_(o). Thus, ifthe thickness of the semiconductor structure is less than 0.2R_(o), thenthe efficiency of the laser cathode-ray tube will decrease considerablybecause some part of the excitation energy will penetrate into thesubstrate and will be converted entirely into heat.

Note also that the structure thickness does not need to be very large.It is preferable that it is less than 2 R_(o). If the structurethickness is more than 2 R_(o), then it will result in the increase inthe threshold of the laser target because of the increase in losses inunpumped part of the structure and the increase of diffraction losseswhich, in turn, will result in decrease of efficiency of the lasercathode-ray tube.

To decrease a laser threshold, the thicknesses of active and passivelayers should be mutually adapted so that nonequilibrium carriesgenerated by the electron beam concentrate into active layers withmaximum density. For this purpose, the thickness of an active layershould be less than the passive layers adjacent to this active layer,and the thickness of any passive layer should be less than a path lengthof the nonequilibrium carriers generated by electron beam in the passivelayer.

Since one of the surfaces of laser target in laser cathode-ray tube isirradiated with a scanning electron beam and the thickness of thesemiconductor structure is low, then the heat produced in the structurecan be transmitted to the substrate through only one of the mirrorslocated between the substrate and the structure. Therefore, in order toimprove heat-dissipation it is advisable to make the activesemiconductor medium and at least one of the mirrors facing thesubstrate entirely as a heterostructure.

To further improve heat-dissipation and to also increase the lifespan ofthe laser target, and hence of the laser cathode-ray, tube the use of amonocrystalline substrate is suggested, wherein one of the mirrors andthe semiconductor medium are coherently grown on it, so that the crystallattice period of the substrate along the surface of the laser targetmatches the crystal lattice period of the mirror and semiconductormedium.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to specificnon-limiting embodiments of the invention illustrated in theaccompanying drawings, in which identical details are shown at identicalreference numerals and in which:

FIG. 1 represents the general view of the laser cathode-ray tube inaccordance with one embodiment of the invention;

FIG. 2a is an enlarged view of a portion of the laser target of FIG. 1;

FIG. 2b is an enlarged view of a portion of the laser target of analternative embodiment of a laser cathode-ray tube constructed accordingthe invention;

FIG. 3 is an enlarged view of a portion of the laser target of a thirdembodiment of a laser cathode-ray tube constructed according theinvention;

FIG. 4 shows a graphic representation of distribution of the energybandgap E of the semiconductor structure of the laser target of FIG. 3along a normal to the surface of the laser target;

FIG. 5 shows a graphic representation of distribution of the energybandgap E of the semiconductor structure along a normal to the surfaceof the laser target in accordance with another embodiment of theinvention;

FIG. 6 shows a graphic representation of distribution of the energybandgap E of the semiconductor structure along a normal to the surfaceof the laser target in accordance with the embodiment of the inventionin which the varizone semiconductor structure is used;

FIG. 7 shows a graphic representation of distribution of the energybandgap E of the whole laser target along a normal to its surface inaccordance with the embodiment of the invention in which the crystallinesubstrate and the crystalline partly transparent mirror with crystallattice matched with crystal lattice of the semiconductor structure areused, and in which the structure layer thicknesses are adapted to acurve shown schematically in FIG. 7 how the energy E of electrons isabsorbed in the target.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a laser CRT according to the invention has a sourceof electrons 1 as a triode electron gun, a means of controlling theelectron beam 2, which includes an electrostatic modulator 3, a focusingsystem 4, a deflecting system 5, and a laser target 6, consisting of anoptical resonator made of mirror covers 7 and 8, a semiconductorstructure 9, and a transparent substrate 10. The laser CRT may be madeas a sealed-off tube and its single elements are placed either in avacuum outside of it, as shown on FIG. 1. The laser CRT, however, can bemade as a demountable system similar to an electron microscope. Specificdesign of the laser CRT and its elements 1-5 is not the subject of theinvention. The herein invention concerns laser target 6 whose design,however, depends on energy of electrons of the electron beam 11irradiating the target 6 and also on the type of the output of the laseremission 12 from the target 6. Laser emission may have output throughthe substrate 10 (transmission-type tube), and in this case thesubstrate must be transparent and thermoconductive, or through themirror 7 (reflection-type tube). In the latter case, the substrate doesnot necessarily have to be transparent but the output of the laseremission from the vacuum space would be considerably hampered.

The laser CRT works in the following way. The source of electrons 1forms slightly diverging electron beam 11 which current is modulated bythe electrostatic modulator 3, focused by the focusing system 4, anddeflected into the given point on the laser target 6 by the deflectingsystem 5. Penetrating through mirror 7, electron beam 11 generatesnonequilibrium electron-hole pairs in the semiconductor structure 9.Cathodeluminescence and optical amplification arises in structure 9 andin the presence of the optical resonator formed by mirrors 7 and 8. As aresult, there occurs the generation of laser ray 12 emerging from thevacuum space through the transparent substrate 10.

With reference to FIGS. 2a and 2b, the laser targets the embodiments ourinvention have the semiconductor structure 9, placed into the opticalresonator formed by mirror covers 7 and 8 and fastened with a fasteninglayer 13 to substrate 10, contains elastically strained elements of atleast two types. Element 14 is made of narrower gap compound and element15 of wider gap compound. There can be different types of forms of theseelements depending on the field of use of the laser CRT. Elements 14 maybe flat layers oriented in the plane yz (as in the FIG. 2a where axis yis perpendicular to the plane of the Figure), or in the plane xz, or inthe plane xy (see below FIG. 3) or in the some other plane, separated bysimilar flat but usually thicker layers element 15.

Element 14 may also be made as limited along all the axes of threedimensional figures, such as parallelepipeds, cubes, spheres, drops,etc. as shown in FIG. 2b, with element 14 embedded into themedium-element 15. In all cases boundaries between the elements 14 and15 are coherent according to the invention. The condition of coherencyof the boundaries sets practical limitations on the requirementsregarding the sizes of elements 14 and 15 when made of materials, thathave crystal lattice parameters which differ in a free state. With anincrease in this difference, sizes of the elements 14 and/or 15 decreasein at least one of the directions. When the difference in the latticeparameters is more than 10%, sizes of the elements 14 or 15, in at leastone of the directions, cannot be greater than one monolayer.Particularly crystals of solid solutions of some compounds may beconsidered as structures with strained elements. Thus, for instance, inthe crystals of solid solution CdS_(1-x) Se_(x), the distance betweenthe atoms of cadmium and selenium is somewhat increased in comparison tothe case of pure CdSe, and the distance between Cd and S on thecontrary, is decreased. In this case, strained elements are separatechemical bondings.

Elements 14 and 15 can also form a superlattice in which a spatialdependence of an energy gap have translational symmetry of the formEg(r+q)=Eg(r) where q=n₁ ·a₁ +n₂ ·a₂ +n₃ ·a₃ ; where, n₁, n₂, n₃ are thewhole integers and, a₁, a₂, a₃ are the basis vectors of elementary cellof the crystal. These can be one-dimensional, two-dimensional, andthree-dimensional superlattices.

Note that the elements 14 and 15 do not necessarily have to be made ofcompounds with different energy gaps in a free state. However, in thiscase is preferable that these component being parts of semiconductorstructure 9, and being in the strained state, have necessary differenceof the energy gap.

The design of the semiconductor structure with at least two types ofelements 14 and 15 is necessary, on one hand, for arranging electron andoptical confinements in order to decrease the lasing threshold andimprove the other characteristics of laser target what is widely used ininjection lasers. On other hand, it is better for matching of thecrystal lattice parameters of the semiconductor structure 9 on theboundaries with crystal mirrors 7 and 8 and, even substrate 10.Generally, mirrors 7, 8, substrate 10, and fastening layer 13 may be noncrystal or non lattice-matched. However, for the improvement of theCRT's lifespan and for increasing the average power of radiation bymeans of an increase in heat dissipation of the semiconductor structure9 and also for simplification of the manufacturing technology, it isworthwhile to make at least one of the mirrors and/or substrate andfastening layer crystalline and lattice-matched with each other and withthe semiconductor structure. Note that lattice-matching can be achievednot only by designing the semiconductor structure 9 of several strainedelements, like elements 14 and 15, but also by means of designing themirrors 7 and 8, as well as the substrate 10 and fastening layer 13 toconsist of their own strained elements.

The simplest example of the preferred embodiments in terms ofmanufacturing of the laser target is shown on the FIG. 3. In this case,the semiconductor structure 9 consists of alternating strained elements16 and 17 made as layers perpendicular to the axis z, which is thelongitudinal optical axis of the resonator, formed by the mirror covers7 and 8, which in turn, consist of alternating layers 18, 19 and 20, 21.The semiconductor structure 9 is made as a plate attached to thesubstrate 10 from the side of mirror cover 8 through fastening layer 13.

The number of types of the strained elements of the semiconductorstructure can be more than two. Moreover, they do not need to alternate.All of them could have different compositions and thicknesses, as well.In particular, a separate layer may have the thickness of one monolayer.However, for simplicity of manufacturing, it is worthwhile to make thesemiconductor structure with a small number of different alternatinglayers with constant thicknesses, forming a one dimensionalsuperlattice.

Strained layers 16 and 17 may be made of semiconductor II-VI or III-Vcompounds, or its solid solutions differing in the energy gap by atleast 7 mev.

The distribution of the energy gap Eg of the semiconductor structure 9along the z-axis in accordance with one embodiment of the invention isshown on FIG. 4. Strained layer 16 with the narrower energy gap is anactive layer and has the thickness h₁, and the strained layer 17 withwider energy gap is a passive layer and has the thickness h₂, so asuperlattice with period H=h₁ +h₂ is formed.

With reference to FIG. 5, the superlattice of the semiconductorstructure is formed by four layers with thicknesses h₁, h₂, h₃, h₄ andenergy gaps Eg₁, Eg₂, Eg₃. In some cases, use of two additional layerswith the intermediate energy gap E around the active layer with thelowest E allows for the achievement of a more efficient electronconfinement (to achieve larger concentration of nonequilibriumelectron-hole pairs in active layers), which in turn allows the decreasethe lasing threshold and the improvement of other characteristics of thelaser target.

If one increases number of intermediate layers it is then possible tocome to a different design of the semiconductor structure, namely avarizone superlattice which energy gap distribution represented in theFIG. 6. The varizone superlattice is not worse than discrete ones inmany parameters but it can be made using simpler and more economicaltechnologies, such as chemical vapor deposition (CVD). Discretesuperlattices, on the other hand, can be grown by only lower temperatureepitaxy as metallo-organic chemical vapor deposition (MOCVD) ormolecular beam epitaxy (MBE).

Mirror covers 7 and 8 can be made as single layer consisting mainly of ametal that allows it to achieve a high reflection coefficient (silver,aluminum), or as a plurality of alternating transparent mainlyquarter-wave layers with greater (layers 18 and 20) and lower (layers 19and 21) refraction indices (see FIG. 3), or the combination of bothmetal and transparent layers. In the case of a transmission-type tube asshown in the FIG. 3, when the generated irradiation hv emerges from thelaser target through the substrate 10, the fastening layer 13 andsubstrate 10 must be at least partly transparent, mirror cover 8 partlytransparent (transparency from 1 to 20%), and the mirror cover 7 must bemainly high-reflecting. In the case of the reflection-type tube, whenthe generated irradiation hv emerges through the mirror cover 7, thefastening layer 13 and substrate 10 may be non transparent, forinstance, made of metal, mirror cover 7 is partly transparent, andmirror cover 8 is mainly high-reflecting. Mirror covers 7 and 8 areusually made amorphous. For their manufacturing one often uses vacuumsputtering of metal or oxides, such as SiO₂, ZrO₂, TiO₂, Al₂ O₃, HfO₂,et al.

Fastening layer may be made as glue layer, for instance of epoxy glue ofOK-72 F type (Russian type), or as a glass layer. Substrate is usuallymade of highly thermoconductive material: sapphire or garnet for atransmission-type tube or copper, silicon, etc. for reflection-typetube.

To improve heat-dissipation and increase a CRT's lifespan, it isworthwhile to make crystalline at least one of the mirror covers 7 or 8,substrate 10 and fastening layer 13. In this case, it is not necessaryto fulfill the condition of coherency of the boundaries between themirror covers 7, 8, semiconductor structure 9, fastening layer 13, andsubstrate 10. This is because the existence of structure defects outsidethe semiconductor structure 9 does not directly affect the powercharacteristics of the laser target. However, these defects may be asource of new defects that "grow" into the structure during exploitationof the laser target and worsen the characteristics of the laser targetmainly by decreasing its lifespan. Therefore it is worthwhile that thesubstrate 10 is single-crystalline and the mirror 8 between thesubstrate 10 and semiconductor structure 9, and the semiconductorstructure 9 itself are coherently grown on it, while the crystal latticeperiod of the substrate along the surface of the laser target matchesthe crystal lattice period of the mirror 8 and semiconductor medium 9.It is even better if the mirror 7 has the same properties.

Laser targets of the cathode-ray tubes that are used for differentpurposes are pumped by an electron beam with an energy that ranges from30 to 100 kev. Each primary electron of the high energy, penetratinginto the laser target, moves in it piecewise. An straighten path lengthof the electron R_(o) depends on the average atomic number of thestructure, on the density of this structure and the energy of theelectron. Specific excitation depth of the structure is about 0.2 R_(o).Therefore, thickness of the semiconductor has to be not less than thisvalue, otherwise, more than 50% of electron beam energy would not beused for creation of the nonequilibrium carriers, and the efficiency ofthe laser target emission would decrease. The thickness of semiconductorstructure could be larger than 0.2R_(o), although if it exceeds 2 R_(o),then the lasing threshold increases because of an increase ofdiffraction losses at excitation by a sharply focused e-beam, andtherefore the efficiency of the laser screen decreases. For the electronenergy of 30 to 100 keV and the use of II-VI and III-V compounds, thevalue R_(o) is about from 10 to 75 μm. So it is preferable that thethickness of the semiconductor structure will be from 2 to 20 μm for 30keV and from 15 to 150 μm for 100 keV.

The thickness of the metal mirror cover usually does not exceed 0.1 μmand practically does not decrease the excitation depth of thesemiconductor medium when it covers the radiated surface of the lasertarget (mirror 7). The thickness of the interference multilayer covermade of 6 to 8 alternating quarter-wave layers SiO₂ and TiO₂ withreflection coefficient R≈90% usually does not exceed 1 μm. However, ifthe mirror is made crystalline, then adjacent alternating layers musthave similar crystal structures, and this usually leads to a smalldifference in the refractive index. For this reason the number of layersin the crystal mirror must be greater by the order of magnitude andtheir total thickness may reach 10 μm or even more. The use of a passivemirror, such as a bombarded one, is not practically possible because itsthickness is comparable with excitation depth at energy 75 keV. However,there is a possible variant when the semiconductor structure performssimultaneously the functions of at least one of the resonator mirrors.In this case, at least part of one of the alternating layers of themirror is optically active.

Note also that thickness of one of the alternating quarter-wave layersof the mirror is about 60 to 80 nm. In order for the mirror to havecoherent boundaries between the layers (which, as it was mentionedabove, increases the CRT's lifespan), mismatching of the crystal latticeparameters of the adjacent layers must be very little, about 1% andless. This drastically decreases the number of compounds that may beused for manufacturing the mirrors. Thus, in order to broaden this setof compounds, it is worthwhile to make at least one type of thequarter-wave layers a superlattice. For example, quarter-wave layerswith a lower refractive index are made of ZnS/CdS-superlattice withperiod of several monolayers.

The substrate is usually made thick for providing sufficient mechanicalstrength that can stand atmosphere pressure overall with the diameter ofup to 60 mm and providing for sufficiently effective heat removing,especially if the heat is removed through the side surface of thesubstrate. In that way, its thickness is from 1 to 20 mm. In an idealcase, when the semiconductor structure 9, mirror 8, and substrate 10have coherent boundaries, crystal lattice period of the laser targetalong its surface is practically determined by the crystal latticeperiod of the substrate because the substrate is considerably thickerthan the other elements of the laser target.

The variant easier to realize is when the lattice of the substrate 10does not match the one of the semiconductor structure 9. In this case,fastening layer performs the functions of a buffer layer that hasstructure defects of mismatching dislocation type but matches crystallattices of the mirror 8 and substrate 10. In particular, a superlatticewith strained layers also may be used as a buffer layer. Fastening layer13 may be non-crystal (in this case it indeed only fastens) if thesubstrate 10 is non-crystal and/or it is not used as a substrate in thegrowing process of the semiconductor structure 9.

The graph shown on FIG. 7 is the distribution of energy gap of wholelaser target along z-axis for the most preferable embodiment inaccordance with the invention. The corresponding laser target has themetallic mirror cover 7 (Eg=0) of the thickness h_(m1), the strainedlayer semiconductor structure 9 of the thickness h_(str), the multilayercrystalline mirror cover 8 of the thickness h_(m2) and the crystallinesubstrate 10 of thickness h_(sub) in the absence of the fastening layer13. The thicknesses of active structure layers having narrower gap andconstant thickness, and passive structure layers having wider gap andvariable thickness and variable composition, are adapted with anionization curve of energy losses of the electron beam δE/δz, are alsoshown in FIG. 7, so that total thickness of two adjacent layers altersalong the z-axis inversely proportionally to the fraction of theelectron beam absorbed by these two layers. The composition of eachpassive layer is adapted with its thickness so that boundaries betweenthis passive layer and adjacent active layers are coherent. Themultilayer crystalline mirror cover has a plurality of alternatingquarter-wave layers with high (thickness h_(h)) and lower (thickness h₁)refractive indices, the superlattice serving as the layers with thelower refractive index. The boundaries between all layers of themultilayer crystalline mirror are coherent too. The crystal latticeperiods of the structure, the crystalline mirror and the substrate arematched each other.

In operation of the laser target, nonequilibrium electrons and holesgenerated by the electron beam 11 in the excitation region 22 in FIG. 3are collected in the layers with narrower energy gap, in the potentialwells (where electron confinement occurs). Thus, the high density of theelectron-hole pairs, that leads to an optical amplification, isachieved. If there is no electron confinement, then the lasing thresholdincreases and irradiating characteristics of the laser target get worse.The density of the electron-hole pairs collected in potential wellsdepends on the volume of the crystal around these wells where they arecollected from, and on the quantity of the energy losses of the electronbeam in this volume. Because the energy losses change along the depth ofthe crystal according to the ionization curve (δE/δz in FIG. 7), then inorder to equalize the number of the nonequilibrium electron-hole pairscollected in each well, the thickness of the wider-gap layers should bechanged in concordance with this curve. If the thickness of these layerswas not changed according to the ionization curve, then a differentnumber of nonequilibrium electron-hole pairs would be collected indifferent potential wells. This would lead to inhomogeneous broadeningof the gain spectrum and resulting finally in an increase of the lasingthreshold and a decrease in brightness of irradiation of the lasertarget.

The ionization curve δE(z)/δz in FIG. 7 does not have exact analyticdescription but it may be approximated with sufficient precision by theGaussian distribution (see B. M. Lavrushin "Research of SemiconductorQuantum Generators on GaAs Basis." Proceedings of P. N. Lebedev PhysicsInstitute. Vol. 59, M., Nauka, 1972, pp.124-205):

    δE(z)/δz=A.sub.0 ·exp (z-a).sup.2 ·b.sup.-2 !(2)

where A is a density of ionization losses in maximum of distribution atz=a; constants A , a, and b for GaAs are:

    a=2.3·10.sup.-2 ·E-5.4·10.sup.-4 ·E.sup.2, μm;                                 (3)

    b=3.2·10.sup.-2 ·E-7.6·10.sup.-4 ·E.sup.2, μm;                                 (4)

    A.sub.0 =2(0.116+2.7·10.sup.-3 ·E), keV/μm;(5)

where E is the energy of the electron beam expressed in keV.

If the thickness of the layers of the semiconductor structure 9 withconstant composition h and the thicknesses of the other layers h(z) aremuch less than the parameters of the ionization curve a and b thanaccording to the invention, then it is worthwhile to choose thicknessesof the layers from the condition:

    h.sub.2 (z)+h.sub.1 =const/(δE(z)/δz)          (6)

then for the approximation cited above

    h.sub.2 (z)=(h.sub.2o +h.sub.1)·exp (z-a).sup.2 ·b.sup.-2 !-h.sub.1                                                 (7)

where constant h_(2o) =h₂ (z=a) is chosen simultaneously withconsidering achievement of required electron confinement and alsonecessary quantization in potential wells.

In order for this structure to not have structure defects which worsenthe irradiating properties of the laser target, it is necessary thatcrystal lattice period of all layers be the same along the layers. Thisis the condition of coherency of the boundaries. In the structure withlayers of different thicknesses, this condition is fulfilled ifcomposition of the layers changes in concordance with their thicknesses.Let the layers of the semiconductor structure 9 in FIG. 7, that haveless width of energy gap and thus are potential wells, be made of thefirst binary compound A₁ B₁ and the layers with a variable composition,being the barriers, be made of solid solution of compound A₁ B₁ andsecond binary compound A₂ B₂. The layers with constant composition havethickness h₁, the crystal lattice period along the layer in free stateis a₁, and the elastic stress X_(x) along the layers is proportionalwith coefficient G₁ to the period change Δ a₁ (X_(x) G₁ ·a₁); and layerswith variable composition have thickness h(z), the corresponding periodis a₁ =a₁ +(a₂ -a₁)·x and the corresponding coefficient G(z)=G₁ +(G₂-G₁)·x, where a₂ and G₂ belong to compound A₂ B₂. Then condition ofcoherency of the boundaries is expressed by expression (Y. Kawakami, T.Taguchi, and A. Hiraki. J. Crystal Growth. 1988. Vol.93. pp.714-719):

    (G.sub.1 ·h.sub.1 ·a.sub.1 +G·h·a)/(G.sub.1 ·h.sub.1 +G·h)=a'(8)

or ##EQU1## where a' is the period of crystal lattice along layers forwhole semiconductor structure 9. From this expression one can obtain therelationship between x and h(z):

    x=C·{ 1+D·(1+h.sub.1 /h(z)).sup.0.5 !-1} (10)

where;

    C=0.5· G.sub.1 /(G.sub.2 -G.sub.1)-(a'-a.sub.1)/(a.sub.2 -a.sub.1)!(11)

    D=2/C/ (a.sub.2 -a.sub.1)/(a'-a.sub.1)-(G.sub.2 -G.sub.1)/G.sub.1 !(12)

Taking into consideration that a' alters in a range from a₁ to a₂ and(G₂ -G₁)/G₁ alters from 0.1 to 0.25 for the majority of II-VI compounds,we obtain that C may have values from 2 to 4.5, and D from 0 to 1.5. Forother compounds, the range of values of C and D may be considerablywider.

The more detailed description of a laser CRT utilizing the materialsmentioned above is given below by some examples. In these examples,however, materials, dimensions and other operating parameters areprovided by way of illustration only, and, unless otherwise expresslystated, are not intended to limit the scope of the invention.

EXAMPLE 1

The laser cathode-ray tube contains known type of electron beam source 1with an accelerating voltage of 75 keV and a means 2 for its controllingand new laser target 6. The laser target 6 has the first mirror 7 madeof silver layer 0.08 μm thick, a semiconductor structure 9 having twoparts, a second mirror 8 made of six alternating quarter-wave layers ofSiO₂ and ZrO₂, an epoxy fastening layer 13 having a thickness of 10 μmand a sapphire substrate 10 having a thickness of 2 mm.

The first part of the semiconductor structure having thickness of 10 μm(which is comparable to the depth of excitation by electron beam) andbeing adjacent to the mirror 7 is made of superlattice formed byalternating strained layers 16 and 17. The passive layers 17 areconstructed of ZnS, have a thickness of 2.0 nm and act as a barrierlayers. The active layers 16, which are constructed of CdS, have athickness of 3.4 nm and act as quantum wells.

The second part of the semiconductor structure is a thick passive layer23, which is located between the first part 9 and mirror 8. Thick layer23 has a thickness of 30 μm and is made of compound comprised of Zn₀.43Cd₀.57 S. The lattice parameter of the second part of the semiconductorstructure along the layers is a=5.653 A and is equal to the latticeparameter along the layers of the superlattice mentioned above. Notethat this second part is also a passive layer like layers 17, but itdiffers in that it is thicker and is practically non-strained.

The laser target may be made in the following way. The super-lattice ofthe alternating strained ZnS-layers 17 (2.0 nm thickness) and CdS layers18 (3.4 nm thickness) having a total thickness of 10 μm is coherentlygrown on the GaAs-substrate by the low-pressure MOCVD method describedin the article Y. Endoh et al. "Structural and PhotoluminescenceCharacterization of CdS/GaAs Films and CdS-ZnS Strained-LayerSuperlattices Grown by Low-Pressure MOCVD Method", Jap. J.Appl.Phys.,1988, Vol.27, pp. L2199-L2202. Then the thick passive layer 23 of Zn₀.43Cd₀.57 S (30 μm thickness) is grown on the super-lattice byatmospheric-pressure organometallic vapor-phase epitaxy (OMVPE)described in the article S. Fujita et al. "Organometallic Vapor-PhaseEpitaxial Growth of Cubic ZnCdS Lattice-Matched to GaAs Substrate",J.Cryst. Growth, 1990, Vol.99, pp.437-440. Since the lattice parametersGaAs, superlattice, and passive layer 23 are the same along the layers,then the resulting heterostructure practically does not have structuredefects of mis-matching dislocation type. The interference mirror 8 ofsix alternating layers of SiO₂ and ZrO₂, is put onto the thick passivelayer by the known method of vacuum sputtering. Further, the structurewith interference mirror cover 8 is then glued to a sapphire disk 10using epoxy glue OK-72F(Russian name). Thus, interference mirror 8becomes located between the semiconductor structure and glue layer.After gluing, the GaAs-substrate is completely etched by the knownetchant H₂ O₂ :N₄ H OH. After etching, a silver cover of 0.08 μmthickness is deposited onto the clear surface of the super-lattice byvacuum sputtering.

For the growth of the superlattice, the MOCVD apparatus consists of avertical cold-wall reactor containing a susceptor heated by a RF radiantheater. Cr-doped semi-insulating (100) GaAs wafer is used as a growthsubstrate. After chemical etching in a H₂ SO₄ --H₂ O₂ --H₂ O 5:1:1mixture, followed by in 10% Br methanol, the GaAs-substrate isimmediately set onto the susceptor and the reactor is evacuated at1·10⁻⁷ Torr. Prior to deposition, the substrate is thermally cleaned at550° C. in H₂ atmosphere for 5 minutes to remove the residual oxidizedlayer. Dimethylzinc (CH₃)₂ Zn, DMZn, 1%! diluted in He gas withconcentration of 1% and dimethylcadmium (CH₃)₂ Cd, DMCd, 0.1%! are usedas the metalorganic alkyl source materials together with 10% H₂ S in H₂gas for the epitaxial growth. Substrate temperature is 300° C., flowrate of DMCd, DMZn, and H₂ S are 5.80·10⁻⁶ mol/min, 6.70·10⁻⁶ mol/min,1.34·10⁻⁶ mol/min, respectively. Pressure is 0.6 Torr. Growth time ofeach layer is controlled by a computer.

For the growth the thick passive layer 23, the OMVPE apparatus is likethe MOCVD one but simpler. The semiconductor substrate and itspreparation are described above. However, different source gases areused. They are diethylzinc (DEZn), dimethylcadmium (DMCd), andmethylmercaptan (MSH). Substrate temperature is 420° C., and flow rateof DEZn, DMCd, and MSH are 7.2·10⁻⁶ mol/min, 8.8·10⁻⁶ mol/min, and120·10⁻⁶ mol/min, respectively.

In use the laser target is excited with the scanning electron beam withthe following parameters: energy of the electrons=75 keV, diameter ofthe electron spot=20 μm, e-beam current=1 Ma, scanning speed=10⁵ cm/sec.This yields an irradiation output power not lower than 7.5 W withefficiency not less than 6% and a wavelength=495 nm at T=300° K. At theTV-scanning operating regime, a change in the output power ofirradiation after 10 hours of constant operation was not observed.Unlike any of the known solutions, in the present example, the lasercathode-ray tube with heterostructure laser target irradiates in theblue region of spectrum. Use of the design for a laser target accordingto the invention allows to one increase considerably output power ofirradiation and efficiency of the laser CRT in this region of thespectrum (at T=300° K., not less than by two times) without decrease inthe CRT's lifespan.

EXAMPLE 2

Example 2 is the same laser cathode-ray tube as in Example 1 with thedifference that accelerating voltage of 50 keV is used and the wholesemiconductor structure 9 made as heterostructure with strained layersof 10 μm total thickness (approximately 1500 layers). Every second layeris made of ZnSe and has thickness h_(znse) =1.5 nm. The first layer ofthe semiconductor structure, counting from the mirror 7 of the lasertarget 6 located on the side of the electron beam incidence, and all thefollowing intermediate layers between the ZnSe layers are made of thesolid solution ZnS_(x) Se_(1-x), and have different thicknesses h_(2n+1)and composition parameters of the solid solution x along the axis ofoptical resonator, which values are determined according to thefollowing table:

Construction of the semiconductor medium of ZnS_(x) Se_(1-x) matched tothe ionization curve.

    __________________________________________________________________________    No. of the                                                                    Layer  Layer thickness (nm)     Compound parameter x                          __________________________________________________________________________    1      12.8                     0.92                                          2      1.5                      0                                             2k     1.5                      0                                             2k + 1 7.1                      1                                             2n     1.5                      0                                             2n + 1                                                                                ##STR1##                2.94 { 1 + 0.656 · (1 + n.sub.2n                                     /h.sub.2n+1)!.sup.0.5 - 1}                    Second to last                                                                       1.5                      0                                             Last   470                      0.83                                          __________________________________________________________________________

In this case, the semiconductor structure satisfies the equation (7)with the parameters h_(2o) =4.7 nm, h₁ =1.5 nm, a=2500 nm, and b=3500nm, and the equation (10) with the parameters C=2.94 and D=0.656.

The crystal lattice period of the present structure is chosen in such away that it matches the lattice period of the crystal GaP-substrate withorientation (100)-a'=5.4495 A. This way, the structure described abovemay be grown on GaP-substrate by the same low pressure MOCVD methoddescribed in the Example 1. Of course some details of growing processare different. H₂ Se diluted in H₂ gas with 10% concentration is used asa source for Se, and the flow rates of DMZn, H₂ S and H₂ Se are changedfor each layer.)

The laser target in the Example 2 irradiates at room temperature at thewavelength of 450 nm with the efficiency not less than 8%. This cannotbe achieved by any other known laser in the prior art.

EXAMPLE 3

Example 3 discloses a laser cathode-ray which is similar to Example 1with the difference that in the laser target. Instead of the sapphiresubstrate, the laser uses a substrate of a single ZnSe₀.94 S₀.06 crystalwith orientation (001). The partly transparent mirror of 30 pairs ofalternating quarter-wave layers with higher and lower refraction indicesand the semiconductor structure of super-lattice ZnS/CdS with 10 μmthickness, the structure described in the Example 1, are grown directlyon this substrate by the MOCVD method. Layers with greater refractionindex are made of the same material, ZnSe₀.94 S₀.06, as the substrate,and the layers with lower retraction index are made of the samesuper-lattice ZnS/CdS as the active semiconductor medium.

The laser cathode-ray tube disclosed in Example 3 has approximately thesame characteristics and advantages over the prior art as the onedisclosed in Example 1. But since the laser target in the presentexample does not contain an organic glue layer, the laser CRT with sucha target has certain advantages. It can be exposed to thermovacuumtreatment and therefore may be sealed-off, that allows the devise to besimpler by exclusion of the high vacuum-maintaining system. It will alsoincrease the lifespan of the laser target by the elimination of one ofthe degradation factors, the glue layer, which tends to worsen thetarget characteristics under the exposure of the electron beam andX-irradiation generated by it. Finally, it increases the average outputpower of the irradiation by improvement of the heat removal fromsemiconductor structure by exclusion of the thermal bottleneck caused bythe fastening glue layer.

EXAMPLE 4

The laser cathode-ray tube of Example 4 is similar to the one disclosedin Example 1 except that it uses an accelerating voltage of 25 keV. Alsothe first part of the semiconductor structure has a thickness of 1.3 μmand is comprised of 70 periods of super-lattice with alternatingstrained layers as follows: GaAs-layers having 14 nm thickness acting asbarrier layers and In₀.2 Ga₀.8 As having 4 nm thickness acting asquantum wells. The thick passive layer 23 of the semiconductor structureis made of the single-crystalline GaAs and has 80 μm thickness. Thefirst mirror is made of SiO₂ layer having thickness of 0.21 μm with awavelength=950 nm and is applied to the super-lattice and a Cu-layer of120 nm thickness is applied over the first mirror layer. The secondpartly transparent mirror is made of 13 alternating quarter-wave layersSiO₂ and ZrO₂.

The laser target is made in the following way: super-lattice GaAs/In₀.2Ga₀.8 As is grown on the substrate GaAs of 400 μm thickness withorientation of (100)±30' by the MOCVD method. Kryolit layer having 0.5mm thickness is put on it using the known method of vacuum sputtering.Then the structure is glued by the kryolit surface to the substrate ofC-54 glass (Russian name, it has temperature expansion coefficient of54·10⁻⁷ K⁻¹) of 5 mm thickness by the OK-72F epoxy glue. After thegluing, the product is placed in water to separate the glass substratealong the layer of the hydroscopic kryolit and remove the kryolit fromthe surface of the super-lattice. And finally, the metal-dielectricopaque mirror is applied to the superlattice.

Laser CRT in this example operates with the laser target being at theroom temperature and emitting on wavelength 950 nm. With the current ofthe electron beam of 1 mA, the power of the irradiation equals to 1.8 Wwith 7% efficiency. Such lasing characteristics cannot be achieved byany prior art method.

Given examples do not restrict in any way the set of the materials,constructions and manufacture methods which is covered by the invention.

We claim:
 1. A semiconductor laser comprising:a laser target; a sourceof electron beam and a means for position and time control of saidelectron beam on said laser target to generate a laser beam therefrom,characterized in that said target comprises: a pair of mirrors, at leastone of which is at least partially transparent for said electron beam,forming a cavity resonator at the optical wavelength of said light beam,said control means making said electron beam incident on saidelectron-transparent mirror; a semiconductor structure between saidmirrors, said semiconductor structure comprising at least one activestrained element and at least one passive strained element having widerbandgap than said active strained element, said strained elementsdiffering in crystal lattice parameters in the free state by 0.1% ormore; and, a substrate for supporting said cavity resonator, saidsupporting substrate positioned adjacent to said mirror being oppositeto said electron-transparent mirror; the proportions of said strainedelements of said semiconductor structure being mutually adapted so thatthe boundaries between said strained elements are coherent; theproportions of said semiconductor structure and the energy of saidelectron beam being mutually adapted so that the part of the electronenergy absorbed in said semiconductor structure is not less than 50%. 2.The laser of claim 1 including an evacuable tube, said source beinglocated at one end of said tube and said target at the other end of saidtube, said control means including a electrostatic modulator of thecurrent of said electron beam, a focusing system and a deflecting systemprovided downstream one another in the path of said electron beambetween said source and said target.
 3. The laser of claim 2, whereinsaid supporting substrate is transparent and said light beam emanatesfrom said semiconductor structure and through said substrate inessentially the same direction as said electron beam.
 4. The laser ofclaim 1 including a cooling system, said substrate is connected withsaid cooling system.
 5. The laser of claim 3, wherein said substrate issealed to said other end of said tube made of glass.
 6. The laser ofclaim 1, wherein said strained elements are the strained layers orientedperpendicular to the axis of said cavity resonator.
 7. The laser ofclaim 6, wherein at least one of said strained layers has the thicknessof one mono-layer.
 8. The laser of claim 6, wherein said strained layersof at least part of said structure are the alternating layers withconstant thickness and forming one-dimensional super-lattice.
 9. Thelaser of claim 1, wherein at least part of said strained elements ofsaid structure is made of at least two semiconductor materials selectedfrom the group consisting of II-VI and its solid solutions, saidmaterials differing in the energy width of bandgap by at least 7 mev.10. The laser of claim 1, wherein at least part of said structure ismade of varizone semiconductor compound.
 11. The laser of claim 6wherein every second layer of said structure from saidelectron-transparent mirror downstream in said axis of said cavityresonator is said active layer having a constant thickness and made of asemiconductor compound with constant composition and other layers aresaid passive layers and made of semiconductor compounds, whosecompositions alters in concordance with the thickness of said otherlayers by the value necessary for establishment of common for all saidlayers the lattice period along said layers.
 12. The laser of claim 11,wherein said active layers made of the first compound and said passivelayers are made of the solid solution of said first compound and thesecond compound, while the molar content of said second compound in saidsolid solution in each said passive layer is related to the thickness ofsaid passive layer by the following relation:

    x=C·{ 1+D(1+h.sub.1 /h.sub.2)!.sup.0.5 -1}

wherein x is the molar content of said second compound in said solidsolution; h₁ is the constant thickness of said active layers in nm; h₂is the variable thickness of said passive layers in nm; C is thepositive number depending on the choice of said first and secondcompound and the crystal lattice period of said structure with saidstrained layers along said layers; and, D is the positive numberdepending on the choice of said first and second compound and thecrystal lattice period of said structure with said strained layers alongsaid layers.
 13. The laser of claim 12, wherein said first and secondcompounds are selected from the group consisting of II-VI compounds andits solid solutions.
 14. The laser of claim 11, wherein the totalthickness of two adjacent said active and passive layers changes alongsaid axis of said resonator inversely proportionally to the energy ofsaid electron beam absorbed by said adjacent layers.
 15. The laser ofclaim 6, wherein the thickness of any said active layer is less than thethickness of said passive layers adjacent to this active layer, and thethickness of any said passive layer is less than a path length ofnonequlibrium carriers generated by said electron beam in said passivelayer.
 16. The laser of claim 6, wherein the thickness of saidsemiconductor structure is not more than about two average straightenedpath length of electrons of said electron beam in said structure. 17.The laser of claim 6, wherein said structure is planar and said mirrorsare coated on the opposite sides of said structure.
 18. The laser ofclaim 17, wherein at least one of said mirrors, which is located betweensaid substrate and said structure, is made of crystalline layers, saidcrystalline mirror and said structure are made as a whole crystallinestructure with said strained layers.
 19. The laser of claim 17, whereinsaid substrate is made of single crystal, said mirror located betweensaid structure and said substrate are successively epitaxially grown onsaid substrate, while the crystal lattice period of said substrate, saidstructure, and said mirror are mutually matched along said layers. 20.The laser of claim 19, wherein said substrate is made of crystallinematerial selected from group consisting of II-VI and its solidsolutions, said crystalline material having the band gap wider than oneof said active layers.
 21. The laser of claim 1, wherein at least partof said strained elements of said structure is made of at least twosemiconductor materials selected from the group consisting of III-Vcompounds and its solid solutions, said materials differing in theenergy width of bandgap by at least 7 mev.
 22. The laser of claim 12,wherein said first and second compounds are selected from the groupconsisting of III-V compounds and its solid solutions.
 23. The laser ofclaim 19, wherein said substrate is made of crystalline materialselected from group consisting of III-V compounds and its solidsolutions, said crystalline material having the band gap wider than oneof said active layers.
 24. A laser cathode-ray tube comprising:avacuable tube; a electron beam source including cathode, said sourcelocated near one end of said tube; a laser target located at other endof said tube; a means for focusing and scanning of said electron beam onsaid target to generate a light beam therefrom essentially parallel tothe direction of said electron beam, said target comprising: atransparent substrate sealed to said other end of said tube; a partiallytransparent first mirror on said substrate; a multilayer semiconductorstructure on said first mirror, said structure consisting of alternatingpassive and active strained layers made of II-VI-compounds and its solidsolutions, said active layers having narrower bandgap than said passivelayers, said strained layers differing in crystal lattice parameters inthe free state by 0.1% or more, the thicknesses of said strainedelements of said structure being mutually adapted so that the boundariesbetween said strained elements are coherent; and a highly reflectingsecond mirror on said structure, said mirrors forming a cavity resonatortherebetween; a means for applying to said structure a positivepotential relative to said cathode of said source; said electron beambeing focused and incident on said second mirror so that electronspenetrate through said second mirror into said structure, thereby togenerate said light beam which emanates from said active layers of saidstructure and through said substrate in essentially the same directionas said electron beam; and, the thicknesses of said semiconductorstructure and the energy of said electron beam being mutually adapted sothat the part of the electron energy absorbed in said semiconductorstructure is not less than 50%.
 25. The laser of claim 24, wherein everysecond layer of said structure from said second mirror downstream in theaxis of said resonator is said active layer having a constant thicknessand made of a semiconductor compound with constant composition and otherlayers are said passive layers and made of semiconductor compounds,whose compositions alters in concordance with the thickness of saidother layers by the value necessary for establishment of common for allsaid layers the lattice period along said layers.
 26. The laser of claim24, wherein the total thickness of two adjacent said active and passivelayers changes along the axis of said resonator inversely proportionallyto the energy of said electron beam absorbed by said adjacent layers.27. The laser of claim 24, wherein the thickness of any said activelayer is less than the thickness of said passive layers adjacent to thisactive layer, and the thickness of any said passive layer is less than apath length of nonequlibrium carriers generated by said electron beam insaid passive layer.
 28. The laser of claim 24, wherein the thickness ofsaid structure is not more than about two average straightened pathlength of electrons of said electron beam in said structure.
 29. Thelaser of claim 24, wherein at least one of said mirrors is made ofcrystalline layers, said crystalline mirror and said structure are madeas a whole crystalline structure with said strained layers.
 30. Thelaser of claim 24, wherein said substrate is made of a single crystal,said first mirror and said structure are successively epitaxially grownon said substrate, while the crystal lattice period of said substrate,said structure, and said mirror are mutually matched along said layers.31. A laser cathode-ray tube comprising:a vacuable tube; a electron beamsource including cathode, said source located near one end of said tube;a laser target located at other end of said tube; a means for focusingand scanning of said electron beam on said target to generate a lightbeam therefrom essentially parallel to the direction of said electronbeam, said target comprising: a transparent substrate sealed to saidother end of said tube; a partially transparent first mirror on saidsubstrate; a multilayer semiconductor structure on said first mirror,said structure consisting of alternating passive and active strainedlayers made of III-V-compounds and its solid solutions, said activelayers having narrower bandgap than said passive layers, said strainedlayers differing in crystal lattice parameters in the free state by 0.1%or more, the thicknesses of said strained elements of said structurebeing mutually adapted so that the boundaries between said strainedelements are coherent; and a highly reflecting second mirror on saidstructure, said mirrors forming a cavity resonator therebetween; a meansfor applying to said structure a positive potential relative to saidcathode of said source; said electron beam being focused and incident onsaid second mirror so that electrons penetrate through said secondmirror into said structure, thereby to generate said light beam whichemanates from said active layers of said structure and through saidsubstrate in essentially the same direction as said electron beam; and,the thicknesses of said semiconductor structure and the energy of saidelectron beam being mutually adapted so that the part of the electronenergy absorbed in said semiconductor structure is not less than 50%.32. The laser of claim 31, wherein every second layer of said structurefrom said second mirror downstream in the axis of said resonator is saidactive layer having a constant thickness and made of a semiconductorcompound with constant composition and other layers are said passivelayers and made of semiconductor compounds, whose compositions alters inconcordance with the thickness of said other layers by the valuenecessary for establishment of common for all said layers the latticeperiod along said layers.
 33. The laser of claim 31, wherein the totalthickness of two adjacent said active and passive layers changes alongthe axis of said resonator inversely proportionally to the energy ofsaid electron beam absorbed by said adjacent layers.
 34. The laser ofclaim 31, wherein the thickness of any said active layer is less thanthe thickness of said passive layers adjacent to this active layer, andthe thickness of any said passive layer is less than a path length ofnonequlibrium carriers generated by said electron beam in said passivelayer.
 35. The laser of claim 31, wherein the thickness of saidstructure is not more than about two average straightened path length ofelectrons of said electron beam in said structure.
 36. The laser ofclaim 31, wherein at least one said mirrors is made of crystallinelayers, said crystalline mirror and said structure are made as a wholecrystalline structure with said strained layers.
 37. The laser of claim31, wherein said substrate is made of a single crystal, said firstmirror and said structure are successively epitaxially grown on saidsubstrate, while the crystal lattice period of said substrate, saidstructure, and said mirror are mutually matched along said layers.